Various heat transfer recording methods have been known so far. Among these methods, a dye diffusion transfer recording systems attract attention as a process that can produce a color hard copy having an image quality closest to that of silver halide photography (see, for example, “Joho Kiroku (Hard Copy) to Sono Zairyo no Shintenkai (Information Recording (Hard Copy) and New Development of Recording Materials)” published by Toray Research Center Inc., 1993, pp. 241-285; and “Printer Zairyo no Kaihatsu (Development of Printer Materials)” published by CMC Publishing Co., Ltd., 1995, p. 180). Moreover, this system has advantages over silver halide photography: it is a dry system, it enables direct visualization from digital data, it makes reproduction simple, and the like.
In this dye diffusion transfer recording system, a heat-sensitive transfer sheet (hereinafter also referred to as an ink sheet) containing dyes is superposed on a heat-sensitive transfer image-receiving sheet (hereinafter also referred to as an image-receiving sheet), and then the ink sheet is heated by a thermal head whose exothermic action is controlled by electric signals, in order to transfer the dyes contained in the ink sheet to the image-receiving sheet, thereby recording an image information. Three colors: cyan, magenta and yellow, are used for recording a color image by overlapping one color to other, thereby enabling transferring and recording a color image having continuous gradation for color densities.
Recently, various printers allowing higher-speed printing have been developed and commercialized increasingly in the field of the dye-diffusion transfer recording systems. The high speed print enables to shorten a waiting time when a user obtains a print in a shop. For the foregoing reason, there is a demand for further speeding up of printing.
For the high speed print, it is necessary to convey a heat-sensitive transfer sheet and a heat-sensitive transfer image-receiving sheet at higher speed in a printer. Accordingly, the high speed conveyance results in load of greater torque at the time of both start and stop.
In the heat-sensitive transfer image-receiving sheet, a thick support is used so as to give a sufficient strength to a finished print. Therefore, the image-receiving sheet is heavier than the heat-sensitive transfer sheet, which results in load of greater torque to the image-receiving sheet even though their conveying speed histories are the same. For the reason that a surface of the receptive layer side of the image-receiving sheet is the same as the side on which an image is formed, there arises image defect (failure) owing to friction inside the printer when the heat-sensitive transfer image-receiving sheet is conveyed in the printer. Therefore, the printer is designed in order that such the image defect does not occur. However, the surface opposite to the receptive layer side sometimes gets caught inside the printer in contact therewith. Further, inside the printer a torque is also loaded between the innermost surface of the heat-sensitive transfer image-receiving sheet wound in a roll shape and a shaft unit inserted in the rolled image-receiving sheet. In this area, sometimes slip occurs when a torque is loaded. For the reason that it is difficult to convey the heat-sensitive transfer image-receiving sheet according to the fixed manner because the foregoing “get caught” and slip occur, there arise strain and extraordinary tension in the heat-sensitive transfer sheet. Resultantly, sometimes normal prints cannot be obtained. Therefore, it has been desired to improve such the trouble. The higher the moving speed of the heat-sensitive transfer image-receiving sheets becomes and/or the greater the mass of the heat-sensitive transfer image-receiving sheet wound in a roll shape becomes, the greater the load of torque to the heat-sensitive transfer image-receiving sheet itself and between the innermost surface of the heat-sensitive transfer image-receiving sheet wound in a roll shape and a shaft unit inserted in the rolled image-receiving sheet. Consequently, they become more easily to slip. Therefore, control of slipping properties is a current important problem to be solved.
In order to control the foregoing slipping properties, it is considered to hold a heat-sensitive transfer image-receiving sheet in the state that the image-receiving sheet is wound around a cardboard cylinder, and to individually set suitable physical properties so that an inner surface of the cardboard cylinder is made difficult to slip, thereby to make it difficult to slip between the rolled heat-sensitive transfer image-receiving sheet and a shaft unit, whereas a surface of heat-sensitive transfer image-receiving sheet is made easy to slip, thereby to make it difficult to get caught. With respect to making a cardboard surface difficult to slip, for example, JP-A-62-110997 (“JP-A” means unexamined published Japanese patent application) and JP-A-5-116851 disclose a method of forming an anti-slipping layer, which method includes: coating the cardboard surface with a water dispersion containing a particular latex styrene/butadiene copolymer, polystyrene fine-particles, and a particular polyether compound; and a method of forming an anti-slipping layer, which method includes: coating the cardboard surface with expandable microcapsules in the state of pre-expansion, thereafter producing a cardboard cylinder by employing the thus-coated cardboard, and then foaming the microcapsules by means of heating.
As a result of studies on the inner surface of the cardboard cylinder obtained by any of those techniques, it was found that coefficient of friction was indeed enhanced, but these techniques still caused such problems that anti-slipping effect was insufficient to the instant heat-sensitive transfer print.